Conventionally, in an electrophotographic image forming apparatus that uses an LED head having multiple LEDs arranged in an array, an optical system that forms erect equal magnification images of an object in a line shape is used, and used in this optical system is, for example, a rod lens array where arranged are multiple rod lenses of a cylindrical shape having a refractive index that changes from the central axis toward the outside (for example, see Patent Document 1).